A deployment of 750 Royal Marines is setting off to join the Royal Navy Task Group led by HMS Ark Royal.
The elite troops are being carried on board three Royal Fleet Auxillary landing ships which are leaving from their base at Marchwood port, Southampton, early on Wednesday morning.
The RFA Sir Galahad, Sir Percivale and Sir Tristram will each carry 250 Marines.
The deployment is being sent to the Mediterranean as part of normal exercises, but could be diverted in case of possible war with Iraq.
The three RFA ships will be joined on Wednesday afternoon by a fourth ship, RFA Argus.
The Argus, a 28,000 tonne aviation ship, will carry five Sea King helicopters.
She also doubles as a hospital ship.
A fleet spokesman said: "All four ships will form part of the Amphibious Task Group.
He said: "The landing ships, with Royal Marines embarked, and loaded with vehicles and equipment, will join up with HMS Ocean to head for the Mediterranean.
"RFA Argus, with her large flight deck, hangars and aviation facilities, will also link up with this group.
"She will also be available in her secondary role as primary casualty reception ship." He said.
A total of nine RFA ships will be joining the Task Group in the Mediterranean.